Process for preparing torsemide intermediate

ABSTRACT

The present invention relates to new methods for the synthesis of torsemide and the torsemide synthetic intermediate, (3-sulfonylchloride-4-chloro)pyridine.

CROSS-REFERENCE TO RELATED INVENTIONS

This application is a division of U.S. application Ser. No. 09/812,762,filed Mar. 20, 2001, which claims the benefit of U.S. provisionalapplication Serial Nos. /60/190,650, filed Mar. 20, 2000; and Serial No.60/211,510, filed Jun. 14, 2000, both of which are incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates to new processes for making the torsemideintermediate, (3-sulfonamide-4-chloro)pyridine. The present inventionrelates to new processes for making torsemide.

BACKGROUND OF THE INVENTION

1-Isopropyl-3-[(4-m-toluidino-3-pyridyl) sulfonyl] urea, which has thechemical structure

is approved, under the trademark DEMADEX®, by the U.S. Food and DrugAdministration for the treatment of hypertension and edema associatedwith congestive heart failure, renal disease, or hepatic disease. TheUSAN approved generic name for this compound is torsemide, although thiscompound is also referred to as “torasemide” in the art. Torsemide is aloop diuretic that has been found to be particularly effective for thetreatment of edema associated with chronic renal failure.

The synthesis of torsemide, torsemide intermediates and torsemidederivatives are described in the following references: Delarge, Ann.Pharm. Fr. 31, 467-474 (1973); Delarge, Mem. Acad. R. Med. Belg. 47(3),131-210 (1974); E. Koenigs et al, Chem. Ber. 57, 2080-2082 (1924); L.Thunus, Ann. Pharm. Fr. 33, 487 -494 (1975); Kondo, et al. IyakuhinKenkyu, 25(9), 734-50 (1994); EP 618,209; and U.S. Pat. Nos. 2,516,025;6,674,794; 4,244,950 and Re. 30,633; all of which are incorporatedherein by reference. U.S. Pat. No. 4,244,950 and Re. 30,633, all ofwhich are incorporated herein by reference.

A process for the preparation of the torsemide intermediates(3-sulfonamide-4-chloro)pyridine, 3-sulfomamide-4-(3′-methylphenyl)aminopyridine and torsemide is described in Scheme I.

In known processes where (3-sulfonamide-4-chloro)pyridine is made from(3-sulfonylchloride-4-chloro)pyridine (SCCPY→SAMPCY), the reaction isperformed in a polar solvent, such as, acetone or dioxane, or in meltedreagent as a solvent in the presence of large excess of ammoniumhydroxide. By these known processes, (3-sulfonamide-4-chloro)pyridine(SCCPY), is added dropwise into an aqueous solution of ammoniumhydroxide. The dropwise addition of (3-sulfonamide-4-chloro)pyridineinto an excess of ammonium hydroxide is a method to try to minimize thecondensation of (3-sulfonamide-4-chloro)pyridine with the newly formeddesired product, (3-sulfonamide-4-chloro)pyridine (SAMPCY). These harshreaction conditions necessitate a great effort in purifying theresulting product as well as creating environmental waste disposalissues associated with neutralizing and disposing of large volumes ofconcentrated basic solutions. The highly basic conditions make theprocedures employing a large excess of base very costly. Thus in suchconditions the desired (3-sulfonamide-4-chloro)pyridine is made in lowyields, of about 50%, and is isolated with a high percentage ofimpurities thus requiring additional purification steps. It is desirableto have a process for making (3-sulfonamide-4-chloro)pyridine withoutthe condensation of (3-sulfonamide-4-chloro)pyridine and(3-sulfonamide-4-chloro)pyridine. It is also desirable to have a processfor making (3-sulfonamide-4-chloro)pyridine which gives high yields andhigh purity which is suitable for large scale manufacturing procedures.

In known processes where torsemide is made from3-sulfonamide-4-3′-methylphenyl) aminopyridine, the reaction may beperformed in dioxane or dichloromethane in the presence of triethylamine and isopropyl-isocyanate. Under such conditions the desiredtorsemide is made in low yields and is isolated with a high percentageof impurities thus requiring additional purification steps. The yieldsof these processes are low, highly variable and not are not suitable forlarge scale manufacturing processes. It is therefore desirable to haveprocesses for making torsemide which gives high yields and high puritywhich uses solvents that are suitable for large scale manufacturingprocedures.

SUMMARY OF THE INVENTION

The present invention relates to s process for making a compound of theformula:

comprising the steps of: (a) adding a compound of the formula

to an organic solvent; (b) adding ammonium hydroxide in an amount ofabout 1.75 to about 2.25 mole equivalents; and (c) isolating thecompound of the formula:

wherein X¹ and X² are each independently chloro, fluoro or bromo.

In a preferred embodiment of the present invention, X¹ and X² are bothchloro.

In another preferred embodiment of the present invention, the organicsolvent is selected from the group consisting of t-butyl-methyl ether,toluene, acetonitrile, methyl-isobutyl ketone, ethyl-methyl ketone,acetone, benzene, xylene, ethanol and isopropanol.

In another embodiment of the present intention, the organic solvent ist-butyl-methyl ether.

In another embodiment of the present intention, the ammonia is anaqueous solution.

In another embodiment of the present intention, the ammonia is added tothe solution of step (a).

In another embodiment of the present invention, the ammonia is added inan amount of about 1.75 to about 2.25 mole equivalents

The present invention also relates to a process for making(3-sulfonamide-4-chloro)-pyridine comprising the steps of: (a) adding(3-sulfonylchloride-4-chloro)pyridine to an organic solvent; (b) addingammonia; and isolating (3-sulfonamide-4-chloro)pyridine.

In a preferred embodiment of the present invention, the organic solventis selected from the group consisting of t-butyl-methyl ether, toluene,acetonitrile, methyl isobutyl ketone, ethyl methyl ketone, acetone,benzene, xylene, ethanol and isopropanol. In another embodiment of thepresent intention, the organic solvent is t-butyl methyl ether. Inanother embodiment of the present intention, the ammonia is added as anaqueous solution. In another embodiment of the present intention, theammonia is added to the solution of step (a). In another embodiment ofthe present invention, the ammonia is added in an amount of about 1.75to about 2.25 mole equivalents

The present invention also relates to a process for preparing torsemidecomprising the step of reacting3-sulfonylamide-4(3′-methylphenyl)aminopyridine with isopropylisocyanate in the presence of triethyl amine in a solvent selected fromthe group consisting of acetonitrile, toluene, acetone, ethyl acetateand butyl acetate, and mixtures thereof. In a preferred embodiment ofthe present invention, the solvent is acetone. In another preferredembodiment of the present invention, the solvent is acetonitrile.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to new processes for making the torsemideintermediate (3-sulfonamide-4-chloro)pyridine. The methods of thepresent invention provide for the synthesis of(3-sulfonamide-4-chloro)pyridine in substantially higher yields andhigher purity than previously reported. The intermediate(3-sulfonylchloride-4-chloro)pyridine may be prepared from4-hydroxy-3-pyridine sulfonic acid by methods known in the art,including methods disclosed in Canadian Patent No.: 1,051,888, and J.Med. Chem., 36, 3211-3213, 1993, the content of both are incorporatedherein by reference.

By the methods of the present invention, a compound of formula II′,wherein X¹ and X² are each independently chloro, fluoro or bromo; isadded to a suitable organic solvent (Scheme II). Preferably, X¹ and X²are chloro. Suitable organic solvents include acetonitrile, ethers, suchas, t-butyl methyl ether (MTBE), alcohols, such as, ethanol andisopropanol, ketones, such as, methyl-isobutyl ketone (MIBK), ethylmethyl ketone and acetone; and substituted or unsubstituted aromatics,such as, benzene and xylene. A preferred solvent is t-butyl methylether. Ammonia is then added to the mixture which may cause the mixtureto rise in temperature. Preferably, about 2 mole equivalents of ammoniaare added. Ammonia may be added in the form of gaseous ammonia orammonium hydroxide, and more preferably as an aqueous solution ofammonium hydroxide. Preferably ammonium hydroxide is added as a 25%aqueous solution. The solution is cooled to room temperature and stirreduntil the reaction is substantially complete, e.g., 1 to 1.5 hours,preferably one hour. Completion of the reaction may be monitored by pH;which is indicated when the pH stops decreasing and stabilizes. The pHof the solution is adjusted to about 8±0.1 by the addition of ammoniumhydroxide to induce the precipitation of crystals of the compound offormula III′. The compound of the formula III′ wherein X¹ is chloro,fluoro or bromo; is isolated upon filtering the solution followed bydrying (Scheme II). Preferably X¹ is chloro.

In an embodiment of the present invention, a compound of the formula II,(3-sulfonylchloride-4-chloro)pyridine, is added to an organic solvent.Suitable organic solvents include acetonitrile, ethers, such as, t-butylmethyl ether (MTBE), alcohols, such as, ethanol and isopropanol,ketones, such as, methyl-isobutyl ketone (MIBK), ethyl methyl ketone andacetone; and substituted or unsubstituted aromatics, such as, benzeneand xylene. A preferred solvent is t-butyl methyl ether. Approximately1.75 to about 2.25 mole equivalents of ammonia is then added to thesolution. Preferably, about 2.15 mole equivalents of ammonia are added.Ammonia may be added in the form of gaseous ammonia or ammoniumhydroxide, and more preferably as an aqueous solution of ammoniumhydroxide. Preferably ammonium hydroxide is added as a 25% aqueoussolution. Addition of the ammonia may cause the temperature of thesolution to rise. The solution is cooled to room temperature and stirreduntil the reaction is substantially complete, e.g., 1 to 1.5 hours,preferably one hour. Completion of the reaction may be monitored by pH;which is indicated when the pH stops decreasing and stabilizes. The pHof the solution is adjusted to about 8±1 by the addition of ammoniumhydroxide to induce the precipitation of crystals of(3-sulfonamide-4-chloro)pyridine, the compound of the formula III.(3-Sulfonamide-4-chloro)pyridine, the compound of the formula III, isisolated upon filtering the solution followed by drying. The(3-sulfonamide-4-chloro)pyridine is isolated in a high yield of about74%. By the present methods, the (3-sulfonamide-4-chloro)pyridine isisolated in an unexpectedly high purity of about 93% to about 97%.

Thus, surprisingly the present methods provide processes for making highpurity (3-sulfonamide-4-chloro)pyridine while using a high concentrationof the starting material, (3-sulfonylchloride-4-chloro)pyridine. Incontrast to the known methods, the present methods surprisingly yield(3-sulfonamide-4-chloro)pyridine substantially free of by-productsresulting from the condensation of the starting material and product,(3-sulfonylchloride-4-chloro)pyridine and(3-sulfonamide-4-chloro)pyridine, which is observed in the knownprocesses.

The present method thus provides a new process with high yields and highpurity which is suitable for use in large scale reactions. The highpurity also reduces the need for additional purification steps.

The present invention also relates to a new process for making torsemidefrom 3-sulfonamide-4-(3′-methylphenyl) aminopyridine.3-Sulfomamide-4-(3′-methylphenyl) aminopyridine may be prepared from(3-sulfonamide-4-chloro)pyridine by methods known in the art, includingmethods disclosed in U.S. Pat. No.: 3,904,636, the content of which isincorporated herein by reference.

By the processes of the present invention, a compound of the formula IV,3-sulfomamide-4-(3′-methylphenyl) aminopyridine, is added totriethylamine (TEA) and an organic solvent (Scheme IV). Suitablesolvents are acetonitrile, toluene, acetone, ethyl acetate and butylacetate, and mixtures thereof Preferred solvents are acetonitrile andacetone. A more preferred solvent is acetonitrile. Isopropyl isocyanate(IPIC) is then added dropwise to the solution and the solution is heatedto about 40° C. The resulting mixture is then stirred at about 38° C. toabout 42° C. until there is complete dissolution of all the reactants,about 45 to 90 minutes. The mixture is then cooled to room temperatureand stirred for a suitable time, about 1.5 to about 2.5 hours andpreferably about 2 hours. The pH of the mixture is then adjusted toabout 4.3±0.3, preferably to 4.3 with increasing the temperature toabout 35° C. The pH may be lowered with hydrochloric acid. The mixtureis cooled room temperature, followed by filtration and washing. The wetcrude product is triturated, followed by drying to yield crudetorsemide. The yield of isolated crude torsemide is about 81.5%. Thepurity of the isolated crude torsemide is about 98% to about 99.9% whichis a substantial improvement over the methods known in the art.

EXAMPLES

The present invention will now be further explained in the followingexample. However, the present invention should not be construed aslimited thereby. One of ordinary skill in the art will understand how tovary the exemplified preparations to obtain the desired results

Example 1 Synthesis of (3-Sulfonamide-4-chloro)pyridine

In a 100 mL three necked flask equipped with magnetic stirrer,condenser, thermometer and dropping funnel(3-sulfonylchloride-4-chloro)pyridine (10 g, 1 eq., 46.7 mmoles) wassuspended in MTBE (30 mL) at room temperature. Ammonium hydroxide, 25%solution (13.5 mL, 2.13 eq.) was dropped into the suspension in a ratesuch that the temperature is allowed to increase to about 22 to abut 26°C., this temperature was maintained until all the ammonium hydroxide wasadded. The suspension was then to cooled to room temperature and wasstirred for one hour. The pH of the suspension was adjusted to 8±0.1 bythe addition of a few drops of ammonium hydroxide, 25% solution. Thesuspension was filtered and washed with water (2×10 mL) and the wetproduct (˜8 g) dried at 40° C., under the 1 mm Hg vacuum.(3-Sulfonamide-4-chloro)pyridine was isolated in 74.4% yield, 6.7 g.

Example 2 Synthesis of Torsemide

A 100 mL three necked flask, equipped with mechanical stirrer,thermometer and a condenser was charged with acetonitrile (15 mL),3-sulfomamide-4-(3′-methylphenyl) aminopyridine (5 g), and triethylamine (TEA) (5.3 mL). Isopropyl isocyanate (1.87 mL) was added dropwiseover 10 minutes and the whole mixture was stirred at 40±2° C. tocomplete dissolution. The mixture was cooled to room temperature andstirred for another 2 hours. The pH of the mixture was adjusted to 4.3while increasing the temperature around 35° C. The mixture was cooledagain to room temperature, filtered and washed with acetonitrile:water(1:1) mixture (10 mL). The wet crude product was triturated inacetonitrile:water mixture (5:1, 13 mL) at 60° C. for half an hour,filtered and washed with acetonitrile:water (5:1) mixture (2×7 mL). Thetriturated product was then dried under high vacuum (3 mm Hg) at 50° C.for 6 hours to get 5.4 g of crude torsemide (81.5% crude yield).

Although certain presently preferred embodiments of the invention havebeen described herein, it will be apparent to those skilled in the artto which the invention pertains that variations and modifications of thedescribed embodiment may be made without departing from the spirit andscope of the invention. Accordingly, it is intended that the inventionbe limited only to the extent required by the appended claims and theapplicable rules of law.

What is claimed is:
 1. A process for preparing torsemide comprising thestep of reacting 3-sulfonylamide-4(3′-methylphenyl)-aminopyridine withisopropyl isocyanate in the presence of triethyl amine in a solventselected from the group consisting of acetonitrile, toluene, acetone,ethyl acetate and butyl acetate, and mixtures thereof.
 2. The process ofclaim 1 wherein the solvent is acetone.
 3. The process of claim 1wherein the solvent is acetonitrile.